High-temperature, water-based lubricant and process for making the same

ABSTRACT

A high-temperature lubricant comprising a water-base and minor effective amounts of borate, dextrin, graphite, xanthan gum, and an organic preservative. A powder for preparing a water-based high temperature lubricant is disclosed in which the powder comprises graphite and minor effective amounts of borate, dextrin, and xanthan gum. A continuous process for making the lubricant is also disclosed.

1. This invention relates to a high-temperature, water-based lubricantand, more particularly, to a water-based graphite suspension useful inmetal and mineral forming applications and a continuous process formaking the same.

BACKGROUND OF THE INVENTION

2. Many metal-forming operations are performed at high temperature usingdies, molds and the like. In such operations, lubricants and/or releaseagents are often used to reduce wear on the dies or molds and toprevent-the resulting metal products from sticking to the dies or molds.

3. For example, a fluidized iron ore reduction (FIOR) processing plantincludes a hot briquetting assembly in which direct reduced iron (DRI)briquettes are formed using iron ore fines as a feed stock. Such aprocess is described in U.S. Pat. No. 5,082,251 to Whipp, which isherein incorporated by reference. The briquettes are resistant tooxidation during storage and shipping and can be easily handled andcharged in steel-making operations. In the briquetting process, reducediron ore fines, lumps, or pellets are typically metered from a storagedrum into a briquetting machine, such as those generally described inU.S. Pat. No. 3,988,095 to Mersh et al. and U.K. Patent No. 1,272,617,both of which are incorporated by reference.

4. In a briquetting machine, the material to be briquetted is drawn inby rolls rotating in opposite directions and pressed into briquettes atthe nip between the pair of rolls by means of briquette-shape molds ordies embedded in the rolls. The iron fines, lumps, or pellets enter afeed drum on the top of the briquetting machine and are forced betweenthe two counter-rotating rolls by a feed screw. The rolls are equippedwith briquette-shaped molds which compress the fines into briquettes.The compaction is achieved by a combination of the high pressure betweenthe rolls and the high temperature of the iron feed (approximately 900°C.), which makes them more compressible. Roll temperatures rangetypically between approximately 200° to 450° C.

5. Pressure is maintained by means of hydraulic cylinders that exertforce against one of the two rollers, one roller being fixed and theother being allowed to move in order to prevent breakage should a pieceof metal pass through the machine. The briquettes leave the machine in aweb and then are separated into individual briquettes. The briquettesmay then be quenched in a water-filled tank and discharged onto aconveyor where the moisture is driven off by the heat remaining in thebriquettes.

6. In the past, dry powdered graphite has been used as a release agenton the briquette rolls used for the DRI hot briquetting. However, thedry graphite has not proved satisfactory in that it does notconsistently and uniformly stick to the rolls, resulting in inefficientapplication of the graphite and high loss of the graphite during theapplication, and a concomitant graphite dust control problem. Further,the dry graphite is also relatively abrasive, thus resulting in higherwear on the rolls than is desired.

7. Accordingly, it is an object of this invention to provide a metalworking lubricant and release agent that will both minimize wear on theforming rolls and facilitate the release of the formed metal product.

8. It is a further object to provide such a lubricant that can beefficiently applied to the rolls.

9. It is a still further object to provide a continuous process formaking such a lubricant.

SUMMARY OF THE INVENTION

10. These objects, as well as others which will become apparent uponreference to the following detailed description are accomplished by ahigh-temperature lubricant comprising a water-base and minor effectiveamounts of borate, dextrin, graphite, xanthan gum, and an organicpreservative. Additionally, a powder for preparing a water-based,high-temperature lubricant is disclosed which comprises graphite andminor effective amounts of borate, dextrin, and xanthan gum. Ranges forthe components and preferred embodiments are disclosed for both theliquid lubricant and the powder precursor, as well as processes formaking the lubricant.

BRIEF DESCRIPTION OF THE DRAWINGS

11.FIG. 1 is a schematic representation of a continuous process formaking the lubricant of the present invention.

12.FIG. 2 is an alternative method to that shown in FIG. 1 for makingthe lubricant of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

13. The high-temperature lubricant according to the present invention isexemplified by the following examples showing ranges for the variouscomponents expressed as a percent of the total weight. TABLE 1 ComponentLow (wt %) High (wt %) Tap Water 60.0 80.0 Preservative 0.1 0.3 Borax0.1 1.0 Dextrin 5.0 15.0 Graphite 10.0 30.0 Xanthan Gum 0.1 0.4

14. The tap water can be any water of a quality suitable for industrialapplications, and without harmful impurities. Its purpose is to carrythe solid materials to the work zone and to lower the temperature of thedie due to its evaporation.

15. The preservative can be any material classified as a preservative,such as a biocide, which is suitable for metal working fluids, paints,coatings, and/or suspensions. Its purposes is to protect the organiccomponents of the suspension from micro-biological decomposition.Preferably, the preservative is a 50% solution of glutaraldehyde, suchas Ucarcide 250 preservative available from Union Carbide or Ucar CarbonCompany.

16. The borax may be any material from the inorganic borate chemicalfamily and is preferably sodium tetraborate decahydrate, 10 mole powder.Its purpose is to control the pH of the suspension during storage andhandling and to enhance lubricity. This material may be obtained fromU.S. Borax Co.

17. The dextrin includes all materials from the dextrin chemical family,and is preferably greater than 90% soluble in water. With heat, dextrincooks into a tacky adhesive and finally decomposes into carbon, gasesand ash. Stadex 126 dextrin available from the Staley Co. has providedsatisfactory results.

18. The graphite may be any material from the graphite chemical family,both natural and synthetic, and preferably has an average particle sizeof 30 microns, with a loss on ignition (LOI) of greater than or equal to70%, and more preferably 95% and above. The graphite prevents adhesionbetween the iron briquettes and the briquette mold. In practice, 5033synthetic graphite from Superior Graphite Co. has provided excellentresults.

19. The xanthan gum may be any materials for xanthan gum chemical familyand preferably has a average particle size of 175 microns. Xanthan gumis a suspension agent and prevents the solid particles from settling.The xanthan gum is available from Kelco under the trademark Kelzan.

20. The preferred composition for the lubricant is as follows: TABLE 2Component Wt % Tap Water 69.8 Glutaraldehyde, 50% 0.2 Solution Borax, 10mole powder 0.5 Dextrin, 95-100% water 10 soluble Synthetic Graphite19.3 Xanthan Gum 0.2

21. A powder for preparing a water-based, high temperature lubricantaccording to the present invention is set forth in the following Table3, showing ranges for the various components as a percent of the totalweight. TABLE 3 Component Low (wt %) High (wt %) Borax 0.5 2.0 Dextrin31.0 34.0 Graphite 63.0 66.0 Xanthan Gum 0.5 1.0

22. The preferred composition for the powder is set forth in Table 4.TABLE 4 Components Wt % Borax, 10 mole powder 1.7 Dextrin, 95-100% watersoluble 33.3 Synthetic Graphite 64.3 Xanthan Gum 0.7

23. The lubricant may be made in a batch process using a tank and apropeller-type mixer. Preferably, the suspension is manufactured in aautomated, continuous process, which helps to control costs throughlabor minimization, and the elimination of multiple start-up and shutdown procedures.

24. In one such continuous process, the six raw materials, (the water,preservative, borax, dextrin, graphite and xanthan gum) are used. Withreference to FIG. 1, there is seen a schematic representation of theprocess generally designated 10. The water is collected in a holdingtank 12 and is pumped from the holding tank 12 by a metering pump 14 toa liquid injection point 16. A drum 18 containing the preservative isattached to a metering pump 20, and the preservative is combined withthe water at the liquid injection point 16. The combined stream ofpreservative and water is fed into a powder injector 22. The graphite,dextrin, borax and xanthan gum are automatically unloaded from bulkbags, or similar bulk containers by screw conveyors 24 a, 24 b, 24 c,and 24 d which are associated with the feeder hoppers 26 a, 26 b, 26 c,and 26 d, respectively. The screw conveyors automatically meter therespective ingredients into the powder injector 22, which combines thewater/preservative flow with the other ingredients with a minimum of airentrapment. The suspension is then transported from the powder injector22 by a pump 28 to an in-line high shear mixer 30, which completely wetsthe insoluble solid particles and completely dissolves the solublesolids into the fluid. The suspension is then piped into a container 32,which may be, e.g., a tank truck or large capacity tank.

25. The ratio of the preservative to the water is controlled by themetering pumps 20, 14, while the ratio of the graphite, dextrin, borax,and xanthan gum is controlled by each component's screw feeder rate andthe resulting pump rate from the water/preservative combination. Therates for the pumps 14, 20 and the screw feeders 24 a, 24 b, 24 c, and24 d are controlled by computerized electronic motor frequency controls,which are well known. This general process may also be advantageouslyused for continuously making lubricating suspensions in which thelubricating particles are not graphite, but are other solid lubricants,e.g., borax, boron nitride, molybdenum disulfide, talc, etc. and theliquid in which the lubricating particles are suspended is either water,oil, or other hydrocarbons and/or solvents.

26. In an alternative process, the dry ingredients (the graphite,dextrin, borax, and xanthan gum) are precombined and added to thewater/preservative at the powder injector 22 from a single screwconveyor 34 and feeder hopper 36 (see, FIG. 2). In order to prepare thepowder, a powder blender (not shown) is required. All the components areadded to the blender and are blended together until a uniform mixture isachieved.

27. The water-based, suspended graphite lubricant described above hasfound particular utility in the hot briquetting of iron used in directreduced iron processing plants. Application of the water-suspendedlubricant directly to the dies by spraying has resulted in energysavings due to the reduction in torque energy needed to rotate thebriquetting rolls and has extended roll life by reducing the frictionbetween the rolls and the briquettes. The extended roll life has alsoincreased production due to less down time and maintenance.

28. Spraying has proved to be an efficient method of applying thelubricant to the rolls, with the graphite lubricant binding to the rollsurface after the carrier evaporates. Because the lubricant is waterbased, the evaporation of the carrier is environmentally safe. Further,the use of the water based suspension has reduced the graphite dustcontrol problems associated with the use of dry powered graphite.

29. While the invention has been described as being particularly usefulfor the hot briquetting process, it should also prove equally useful asa die lubricant or mold release in forging and other hot metal andmineral forming operations.

That which is claimed:
 1. A high-temperature lubricant comprising awater base and minor effective amounts of borate, dextrin, graphite,xanthan gum, and an organic preservative.
 2. A high-temperaturelubricant comprising: between about 60 wt % and 80 wt % water; betweenabout 0.1 wt % and 1.0 wt % of borate; between about 5.0 wt % and 15.0wt % of dextrin; between about 10.0 wt % and 30.0 wt % graphite: betweenabout 0.5 wt % and 1.0 wt % xanthan gum; and between about 0.1 wt % and0.3 wt % of an organic preservative.
 3. The lubricant of claim 2comprising approximately 69.8 wt % water; approximately 0.5 wt % borate;approximately 10.0 wt % dextrin; approximately 19.3 wt % graphite;approximately 19.3 wt % graphite; approximately 0.2 wt % xanthan gum;and approximately 0.2 wt % of an organic preservative.
 4. The lubricantof claim 2 or 3 wherein the preservative is a 50% solution ofglutaraldehyde; the borate is a 10 mole powdered borax; the dextrin isbetween 95% and 100% soluble in water; the graphite has an averageparticular size of 30 microns; and the xanthan gum has an averageparticle size of 175 microns.
 5. A powder for preparing a water-based,high-temperature lubricant comprising graphite and minor effectiveamounts of borate, dextrin, and xanthan gum.
 6. A powder for preparing awater-based, high-temperature lubricant comprising: between about 0.5 wt% and 2.0 wt % of borate; between about 31.0 wt % and 34.0 wt % ofdextrin; between about 63.0 wt % and 66.0 wt % graphite; and betweenabout 0.5 wt % and 1.3 wt % xanthan gum.
 7. The powder of claim 6comprising approximately 1.7 wt % borate; approximately 33.3 wt %dextrin; approximately 64.3 wt % graphite; and approximately 0.7 wt %xanthan gum.
 8. The powder of claim 6 or 7 wherein the borate is a 10mole powered borax; the dextrin is between 95 and 100% soluble in water;the graphite has an average particle size of approximately 30 microns;and the xanthan gum has an average particle size of approximately 175microns.
 9. A process for continuously making a water-based lubricantcontaining suspended graphite comprising: supplying water at apre-determined and controllable rate by means of a first metering pump;supplying a preservative at a pre-determined and controllable-rate bymeans of a second metering pump; combining the water and preservativeand injecting the combined water and preservative into a powderinjector; introducing pre-determined amounts of graphite, dextrin,borax, and xanthan gum into the powder injector to combine them with thewater and preservative; pumping the water, preservative, graphite,dextrin, borax and xanthan gum into a high shear mixer; and introducingthe resulting suspension into a container.
 10. The process of claim 9wherein the graphite, dextrin, borax, and xanthan gum are introducedseparately into the powder injector by means of separate metering screwfeeders.
 11. The process of claim 9 wherein the graphite, dextrin,borax, and xanthan gum are combined and introduced into the powderinjector by means of a single metering screw feeder.
 12. A continuousprocess for making a lubricating suspension comprising: supplying aliquid selected from the group consisting of water, oil, hydrocarbonsand solvents at a pre-determined and controllable rate by means of ametering pump and injecting the liquid into a powder injector;introducing pre-determined amounts of a lubricating particles from thegroup consisting of graphite, borax, boron nitride, molybdenum disulfideand talc into the powder injector to combine the powder with the liquid;pumping the liquid and lubricating powder into a high shear mixer; andintroducing the resulting suspension into a container.